How the shell determines that a filename starts with a character ~

Question: How does the shell judge a filename to start with a character ~
Solve:
#var = "cn get the length of me"
#$1:parameter 1 to judge the name of the file
Var=$1
Iscn=false

# ${var:0:2} takes the Var substring from the No. 0 character and takes 22 characters

if [[${var:0:2}-eq ' CN ']]
Then
echo Sub is Chinese ${var:0:2}
Else
echo Sub is 中文版 ${var:0:2}
Fi
#function: Judgment
ISCN ()
{
if [[${var:0:2}-eq ' CN ']]
Then
echo "in ISCN"
Iscn=true
Fi
}

#执行function
ISCN

echo the last IsCN $isCN
=================================================================
First, the shell to pick the substring commonly used:
1)
Echo ${string:1:2}
2 echo $string |cut-c 2-3 (2nd to 3rd characters from string)

Second, the processing of strings

Include: Intercept, connect, match, replace, flip ...
Handling of strings:
1, Intercept
Method One:
echo $a |awk ' {print substr (, 1,8)} '
SUBSTR is a child function in awk that intercepts the first argument, starts with the first character, intercepts 8 characters, and, if not enough, complements the second character.
Method Two
Echo $a |cut-b2-8
Cut: Handle the string of standard input
Cut-bn-m: In byte, starting with Nth Byte, taking m
Cut-bn,m: Intercept the n,m byte in byte
Cut-b-n,m: In Byte, intercept 1-n, and the first m
-C: In Charactor
-D: Specifies the separator, the default is tab
-S: No delimeter in the standard input
CUT-F1: Intercepting domain 1th
Method Three
a=123456
Echo ${string:1:2}
Method Four
Intercept the last two bits of a string using SED
echo $test |sed ' s//(. */)/(.. /)$//'
Intercept the first 2 bits of a string
echo $test |sed ' s/^/(. /)/(.*/)//'
Welcome to visit 007 Computer Information
2, compare
There seems to be nothing to compare.
3, connecting
$a $b
Or
$string
4, flip
Method One:
Use Rev command
Method Two:
Writing a script implementation
#!/usr/bin/awk-f
################################################################
# Description:duplicate Rev in Awk
################################################################
{
Revline = ""
for (i=1;i<=length;i++)
{
Revline = substr (, i,1) revline
}
}
End{print Revline}

5, matching
Grep
Egrep
Fgrep
6, sort
7, replace
In bash:
%x=abcdabcd
%echo $ # replaces only one
Bbcdabcd
%echo $ # Replaces all
Bbcdbbcd
In SH:
。。
How to replace/
Using SED
Replace all matches
echo $test |sed ' S/xx/yy '
Replace a single match
。。
8, get the length of the string:
Bash among
$
Or
Expr "$VAR": '. * '
9, determine if the string is a number
10, get the number of repetitions of a character in the string
echo $a |tr "x" "N" |wc-l
The resulting results need to be subtracted by 1.
or echo $a |awk-f "x" ' {Print NF-1} '
11, get the number of repetitions of a string in 007 computer information
12, replace all strings in a batch of files
For I in File_list
Todo
VI $i <<-!
: g/xxxx/s//xxxx/g
: Wq
!
Done
13, how to insert a character in the middle of every two characters in a string
Using SED
echo $test |sed ' s/. /&[insert char]/g '